1. Field of the Invention
The present invention relates to a photosensitive member for electrophotography, and particularly to a photosensitive member having an electroconductive substrate and a photosensitive layer formed thereon, in which the photosensitive layer contains a novel indole derivative as a charge transporting substance.
2. Description of the Prior Art
Heretofore, photosensitive members for electrophotography have been prepared by using photosensitive substances selected from:
(i) inorganic photoconductive substances such as selenium, selenium alloys, and the like dispersed in resin binders;
(ii) organic photoconductive substances such as poly-N-vinylcarbazole, polyvinylanthracene, phthalocyanine compounds, bisazo compounds, and the like; and
(iii) dispersion of such organic photoconductive substances in resin binders.
These conventional photosensitive members are classified into two types, mono- and multi-layer types, the former comprises a single photosensitive layer, while the latter comprises functionally distinguishable laminated photosensitive layers in which one contributes to generate an electric charge by absorbing irradiated light and the other contributes to transport the electric charge.
In recent years, however, organic photoconductive substances as described above have been put into practical use by virtue of their advantageous features for preparing flexible and light-weight photosensitive members which can be easily mass produced. In addition, there have been much more studies for developing the multi-layer type photosensitive members than the mono-layer one because the former can be easily modified or prepared by using appropriate raw materials so as to have desired or photosensitivities against specific wavelength. Therefore, such photosensitive members have been used in many kinds of electrophotographic devices such as photocopying machines, laser-beam printers, light-emitting diode printers, facsimile machines and the like. More recently, there have been demands for more improved electrophotographic devices, for example a miniaturized device without losing their standard- or high-speed printing or copying abilities. With the technical achievement of the miniaturization, a photosensitive drum to be equipped in such device should be also miniaturized so as to have a smaller diameter and to rotate at a high speed compared with those currently in use. Accordingly, the miniaturized drum may be used more frequently than the normal-size one to make up the printing or recording speed, and thus such drum may be also improved so as to have a high sensitivity against irradiated light and response it at a high speed.
Although the organic photoconductive substances have a number of advantageous features as described above with which inorganic photoconductive substances are not endowed, the fact is that there have been obtained no organic photoconductive substance fully satisfying all the characteristics required of a raw material to be processed into photosensitive member used in the above small-sized electrophotographic device. That is, particular problems involved in the substance have been concerned with a high durability against usage frequency over long period and a high rate of response to illuminated light. To solve these problems, several photosensitive members have been proposed. Most of them comprise functionally distinguishable photosensitive layers. In a document of Japanese Patent Application Publication No. 55-42380, a photosensitive member having functionally distinguished photosensitive layers in which one is a charge generating layer comprising chlorodian blue as a charge generating substance and the other is a charge transporting layer comprising hydrazone compound as a charge transporting substance. A response rate and a durability of this kind of the photosensitive member are mainly depended on the charge transporting layer.
Several substances that can be applicable to the charge transporting layer has been described in the references, for example pyrazorine derivatives disclosed in Journal of Photographic Science and Engineering vol. 21, No. 2, page 73, 1977; enamine derivatives disclosed in Journal of Imaging Science vol. 29, No. 1, page 7, 1985 and Japanese Patent Application Laying-open No. 63-170651; and benzidine derivatives disclosed in documents of Japanese Patent Application Laying-open No. 3-43744 and Japanese Patent Application Laying-Open No. 59-9049.
Under the present circumstances, the conventional charge generating layers do not satisfy the request of providing the photosensitive members with excellent durabilities against usage in frequency over long period and with sufficient rates of response to irradiated light.